Add support for a do-block syntax

[schneiderfelipe]

This adds the proposed in/resolves #32:

julia> using Hyperscript

julia> @tags p

julia> p() do
           "child"
       end
<p>child</p>

julia> m("p") do
           "child"
       end
<p>child</p>

[MarkNahabedian]

Thanks for this. I prefer the do syntax to the argument syntax used by Hyperscript.

How would one add multiple children though?

[schneiderfelipe]

Not sure. I have completely forgotten I coded this. 🤔 Feel free to use it for anything you like though. 🤗